1. Field of the Invention
This invention relates to head-up display systems for aircraft.
2. Discussion of Prior Art
Known head-up display systems present an aircraft symbol and a pitch ladder display. The pitch ladder is a pattern of bars, each drawn (subject to inaccuracies resulting from the sensors and instrumentation) parallel to the actual horizon and forming a scale against which the position of the aircraft symbol indicates a measure of the attitude (pitch) or climb or dive angle of the aircraft. A central bar in the pattern represents zero climb/dive angle in level flight, and it should overlay the actual horizon as seen through the display whenever the horizon comes within the field of view of the display. It follows that the pattern must be tilted, with respect to the display centerline, by minus the bank angle of the aircraft, and the pattern center so placed that the aircraft symbol position gives the desired climb or dive angle measurement when read against the scale formed by the pitch bars. Only a portion of the pattern will be displayed within the field of view at any instant.
In conditions of poor visibility or in aerobatic maneuvers or high turbulence, climb-or-dive angle information is of vital importance. It is of particular importance that whenever the pilot returns his attention to the display after having any distraction or task requiring him to look elsewhere or after any violent maneuver, the display will give him an immediate and accurate appreciation of the bank angle and climb-or-dive angle presented so as to minimize any possibilities of misinterpretation.
The actual horizon, or the central horizon bar in the pitch ladder naturally forms a particularly useful indication by which the pilot can judge the climb-or-dive angle of his flight, but in a climb-or-dive it will soon disappear from the field of view.
When the climb-or-dive angle changes rapidly the bars in a conventional pitch ladder may appear to be written as multiple images and may all too easily be confused. To reduce these difficulties it was suggested in patent GB2179612B that the spacing of the pitch bars should be varied. The present invention is an improvement on the invention of this patent.